The present invention relates in general to electrical control systems and in particular to an apparatus for logically combining, synchronizing and distributing event detection signals for triggering purposes.
Electrical control systems typically employ sensors to produce digital indicating signals on detection of various external events. The indicating signals are then logically combined to produce triggering signals to control triggerable devices. Complex systems may employ many such event detectors to provide the necessary information to control many devices. Often, however, it is not possible to mount event detectors and trigger control circuitry in the same equipment module, such as the same circuit board, and extensive wiring between equipment modules is necessary to interconnect event detection and trigger control circuitry. Further, events and triggers are often synchronous signals within an equipment module with each module having its own independent clock, and it is difficult to synchronize events and triggers associated with different equipment modules.
Multiplexing systems have been developed to reduce the amount of interconnect wiring between equipment modules by converting parallel control signals generated in any one equipment module to serial data for transmission over a single wire pair to remote modules. Such multiplexing has been effective particularly in reducing interpanel wiring between equipment racks in large control systems. However, parallel-to-serial multiplexing systems employ complex circuitry, do not lend themselves to interconnecting triggering signals between many small equipment modules such as circuit boards, and are often unsuitable for high speed operation.
What is needed is a means for interfacing event detectors and triggerable devices mounted on separate equipment modules so as to minimize the interconnecting wiring needed, and for synchronizing differently clocked events and triggers.